Heat oil, a couple of turns of the pan, or butter in a soup pot over medium to medium-high heat. Add carrots, celery, onions, garlic and chili pepper, and season liberally with salt and lightly with black pepper. Cook to soften, 8-10 minutes.
Add spices and stir a minute or 2 then stir in tomato paste and cook a minute more. Add lentils and stock, and bring soup to a boil. Cook until lentils are very tender, 40 minutes or so, wilt in spinach, turn off heat.
While soup cooks, process mint, cilantro and yogurt in food processor or blender into a sauce. Add salt to taste.
Griddle-toast the bread according to package directions then brush bread with melted butter.