Preheat the broiler to high.

Place the tomatillos onto a cookie sheet. Add the jalapeño halves, skin-side-down. Broil until blackened, about 10 minutes. Smaller ones may be blackened before larger ones; they can be taken out sooner while the larger ones continue cooking.

Meanwhile, heat the canola oil in a large skillet over medium heat. Add the onion and garlic. Sauté about 5–6 minutes, until translucent. Add the turkey and beef and cook until the beef is no longer pink, about 7–10 minutes, breaking up the meat with a wooden spoon as it cooks. Add the tomatoes, black beans, sour cream, and taco seasoning. Stir to combine. Heat through and remove from heat.

Preheat oven to 350°F.

Place a heaping cup of the filling on almost the bottom edge of one tortilla. Roll up the tortilla and place, seam-side-down, in a 9- by 13-inch glass or ceramic baking dish. Repeat with remaining tortillas.

Using a pastry brush, brush the top of the tortillas with a little bit of water.

Prepare the salsa verde: Place the blistered tomatillos and jalapeños (do not peel) into the bowl of a food processor fitted with a metal blade. Add the 2 cloves garlic, cilantro, cumin, onion half, and salt. Process until a smooth green salsa forms.

Pour the salsa verde over the enchiladas. Bake, uncovered, for 15 minutes.