Preparation Heat ⅔ cup oil in a large Dutch oven or other heavy pot over medium. Add onion, fennel, celery, and smashed garlic and cook, stirring often, until softened but not browned, 8–10 minutes. Add red pepper flakes, 1½ tsp. paprika, and 1 tsp. salt and stir to combine. Add lentils and 1¼ cups water and stir again, scraping down sides of pot so that all of the lentils are submerged. Lay greens on top of liquid, but do not stir or toss them in. Cover pot, reduce heat to medium-low, and cook until lentils are just cooked through and greens are wilted, 10–15 minutes. Uncover pot and stir mixture a few times to coat greens. Simmer until most of the liquid is evaporated and lentils are saucy (not brothy), about 2 minutes. Squeeze juice of a lemon half into lentils. Taste and season with more salt if needed. Cover and keep warm. Heat 1 Tbsp. oil in a large nonstick skillet over medium-low. Add 2 slices of bread and cook until golden and crisp underneath, about 5 minutes. Transfer to plates and turn fried side up. Repeat with 1 Tbsp. oil and remaining bread. Rub fried side of each slice with remaining whole garlic clove; season with salt. Generously spoon lentil mixture over toast; drizzle with oil and lightly sprinkle with more paprika. Cut remaining lemon half into wedges and serve alongside for squeezing over.