Preheat Oven: Preheat your oven to 375°F (190°C).
Cook Lentils: In a pot, add rinsed red lentils, vegetable broth, tamari, thyme, rosemary, and smoked paprika. Bring to a boil, then lower the heat and simmer for 10-12 minutes until the lentils are tender. Season with salt and pepper to taste.
Prepare Potato and Onion Mix: In a large skillet, sauté the diced onion and garlic until translucent, about 3-4 minutes, then add in the oat flour. After a few minutes, add to lentils.
Layer Ingredients: In a baking dish, spread half of the cooked lentils evenly. Layer half of the sliced potatoes on top, then spread second half of the lentils - finishing with sliced potatoes on top.
Add Tomatoes: Pour the diced tomatoes over the top layer, spreading them evenly across the dish.
Bake: Cover with foil and bake for 40 minutes. Remove the foil and bake for an additional 15-20 minutes until the potatoes are golden and tender.
Garnish: Sprinkle with fresh parsley before serving.