Make the filling. On an ungreased griddle or small, heavy skillet set over medium heat, roast the garlic, turning frequently, until blackened in spots and soft to the touch, about 15 minutes. Cool, peel off the papery skins, then finely chop. Roast the chiles directly over a gas flame or 4 inches below a very hot broiler until blackened on all sides, about 5 minutes for open flame, about 10 minutes for broiler. Cover with a kitchen towel and let stand 5 minutes. Peel, pull out the stem and seed pod, then rinse briefly to remove bits of seeds and stray bits of skin. Chop the chiles into 1/4-inch bits. In a medium-size bowl, mix together the garlic, ricotta, fresh herbs and two-thirds of the chopped chiles. Taste and season with the salt (usually about 1 teaspoon) and pepper (usually about 1/2 teaspoon).
Serve. Sprinkle the remaining poblano over the filling and set out with the radishes, onion, cilantro and warm tortillas for everyone to make tacos.