01 - Heat olive oil in a large pot over medium heat. Add the diced onion, sliced carrots, sliced celery, and minced garlic. Cook for about 5 minutes, stirring occasionally, until the vegetables are softened and fragrant.
02 - Add the rinsed lentils, diced tomatoes with their juice, vegetable broth, bay leaf, dried thyme, smoked paprika, salt, and pepper. Stir to combine. Bring the mixture to a boil, then reduce the heat to low. Cover the pot and simmer for 25 to 30 minutes, or until the lentils are tender. Remove and discard the bay leaf.
03 - While the stew simmers, whisk together the all-purpose flour, baking powder, and salt in a mixing bowl. Add the cold diced butter and rub it in with your fingertips until the mixture resembles coarse crumbs. Pour in the milk and stir gently until just combined. Be careful not to overmix.
04 - Increase the heat under the stew to bring it to a lively simmer. Drop heaping tablespoonfuls of the dumpling dough onto the surface of the stew, spacing them evenly. You should get 8 to 10 dumplings. Cover the pot tightly with the lid and cook for 15 minutes without lifting the lid. The dumplings should be puffed and cooked through.
05 - Taste the stew and adjust the seasoning with additional salt and pepper if needed. Sprinkle with chopped fresh parsley before serving, if desired.