- Preheat oven to 450 degrees F. Heat 1 1/2 tablespoons oil in a medium saucepan over medium-high heat. Add onion and pepper and cook, stirring occasionally, until tender, 4to 6 minutes. Add chili powder and cook, stirring, until fragrant, 30 seconds. Add black beans and 1/3 cup water. Reduce heat to medium-low and cook, stirring occasionally, until thickened, 4 to 6 minutes. Mash beans with the back of the spoon until thick. Stir in lime juice. Season with salt and pepper.
- Meanwhile, toss carrots with cumin and 1 1/2 tablespoons oil on a rimmed baking sheet. Season with salt and pepper. Roast, turning once, until just tender, 10 to 12 minutes.
- Divide beans and carrots between taco shells. Top with avocado, queso fresco, cilantro, and radishes. Serve with lime wedges alongside.
PER SERVING: protein: 8 g; fat: 17 g; carbohydrate: 42 g; fiber: 10 g; sodium: 261 mg; cholesterol: 0 mg; calories: 334.