Addey, All of my recipes are calibrated at or below 300 calories, but I’ll send you some here. If you want to hit 400 calories, just boost the ingredients a bit.

Mussels in Tomato Broth: 293 calories 7.5 g fat 2.4 g fiber 29 g protein 28 g carbs 122 mg Calcium PB GF Another wonderful way to enjoy these best of bivalves.
One pound fresh mussels, cleaned garlic + thyme + parsley 1/4 cup mussel broth ½ cup marinara sauce ½ tsp basil, dried or 1 tsp fresh 2 tsp Parmesan cheese, grated 1 cup lettuce [sliced if leaves are large, not if using baby greens] ½ tsp cider vinegar + ½ tsp olive oil + ¼ tsp Dijon mustard 1 oz French bread [optional]
Put about half an inch of water in a large pot with the garlic, thyme, and parsley. Bring to a boil and add the mussels. Cover an cook for about 15 minutes. Take off the heat and drain, retaining 1/4-1/2 cup mussel liquid in the pan. Stir together the ¼ cup mussel broth and the marinara, along with the basil and Parmesan. Salt and pepper to taste. Put the mussels in a wide bowl, discarding any that did not open. Pour the tomato/broth over the mussels. Toss the lettuce with the dressing and serve the mussels with the bread. Use a spoon to get all the tasty broth at the end.

Baltic Bake: 293 calories 5.5 g fat 7 g fiber 6.6 g fiber 12.8 g protein 33 g carbs 86.4 mg Calcium GF Believe it or not, this diet dinner is from the book Two Fat Ladies Obsessions. The meal has wonderful Eastern European flavors and is so simple to prepare that I assembled it in 16 minutes!!
1.5 low-fat hot dogs [I like Hebrew National reduced-fat] ½ cup canned sauerkraut ¼ c pickled beets, drained ¼ c sliced onions ½ tsp horseradish 2 Tbsp white beans, drained and rinsed
Put the hot dogs [frozen or thawed] and onions in a saucepan with a little water or some juice from the sauerkraut. Heat until the dogs are cooked and most of the liquid is evaporated. Remove the dogs and add remaining ingredients to the pan to heat. Cut the hot dogs into 5-6 pieces and put them back in the pan until all ingredients are heated through.

Chili non Carne: PB GF The recipe is my mother’s, except that she used beef. And she served it on a heap of mashed potatoes, but we won’t do that on a Fast Day.
1 cup =133 calories 0.7 g fat 6.3 g fiber 7.1 g protein 9.8 g carbs 70 mg Ca
1.5 c. =199 calories 1.1 g fat 9.1 g fiber 9.4 g protein 14.2 g carb 120 mg Ca
HINT: This is enough for 4 one-cup servings OR two 1.5 cup servings with 1 cup left over. Save the remaining chili for a lunch or check other postings to see how we use it for breakfast.
For 1.5 cups chili served with cheese garnish and melon, as in photo: 276 calories 9.7 g fat 6.1 g fiber 13.3 g protein 19.4 g carbs 227 mg Calcium
15 oz canned red beans, drained and rinsed 16 oz canned tomatoes – in chunks or diced, not drained 1 cup chopped onion 1 green pepper, chopped 2-3 tsp chili pepper, or more if you like it hotter ½ – 1 tsp ground cumin per serving: 1 Tbsp cheddar cheese, grated, as a garnish 2 oz melon
Saute the onion and green pepper in some of the tomato juices until tender. Add remaining ingredients and cook gently until the stew is thickened. Taste to see if it needs more seasoning. Serve one or one and a half cups for dinner tonight with the grated cheese on top, and melon on the side.

So that’s a seafood meal, a meat meal, and a plant-protein meal. I’ve been doing recipe development for 4 years to adapt/invent new menus for Fast Days. I’ve got A LOT more recipes if you wish.
I will assume that you eat one meal per day on a Fast Day, yes? We eat breakfast and dinner, hence the 300 calorie price tag.
Good luck.