Gather and chop all ingredients. Drain and rinse the black beans.

Heat oil in a large skillet over medium heat. Sauté onions until golden, add garlic, chipotle, cumin, and chili powder; cook for 1 minute.

Add black beans and vegetable stock to the skillet, mash lightly, and simmer for 5-7 minutes. Stir in tomato paste if using, and add lime juice.

Wrap tortillas in a damp paper towel and microwave for 30 seconds or steam them.

Coat a baking sheet with oil, lay tortillas flat, add filling and cheese, fold into tacos.

Preheat oven to 400°F (200°C), bake tacos for 15-20 minutes, flipping halfway through.

Let tacos cool, then serve with toppings like avocado and salsa.