Heat a >3.5 quart (3.3 liters) Dutch oven over medium-high heat. Add 1 tbs. (15 ml) cooking oil and then minced garlic to heated oil. Add diced onions with a dash of salt. Sauté for 3 minutes, until softened and translucent
Add drained lentils and then add 2 cups (472 ml) of stock / broth if you soaked them overnight or 3 cups (705 ml) of stock if not soaked. Add 1 tsp. (5 ml) thyme and 1⁄2 tsp. (2.5 ml) kosher salt. Cover and bring to a boil. Simmer uncovered for 10 minutes if lentils were soaked, 25 to 30 minutes if not soaked
Mix together 1⁄2 tsp. (2.5 ml) dried thyme, shallots, 1 tbs. (15 ml)lemon juice, capers, Dijon mustard, and crème fraiche with 1⁄4 tsp. (1.25 ml) kosher salt
Place fish into a baking pan. Sprinkle with salt and pepper and then cover with mustard mixture. Bake in oven for 12 to 15 minutes depending on thickness of fish
Check if lentils have absorbed all their liquid. Add peas and spinach. Cook for another 2 to 3 minutes and then season to taste with salt and pepper
Enjoy fish with lemon wedges. The mustard / crème fraiche turns into a natural sauce. Serve over lentils