Make the slaw first: In a large bowl combine 3 cups shredded cabbage, 1/2 cup chopped cilantro, the juice of 1 lime (about 1 tbsp), 1 tbsp olive oil, 1/4 tsp salt, and a light pinch of sugar. Toss to coat. Why: Letting the cabbage sit in acid and oil softens it slightly and folds in flavor so the slaw isn’t raw-tasting — it should be bright and crunchy, not bitter.

Add pickled onions: Stir in 3/4 cup pickled red onions to the slaw and taste. Why: The pickled onions add an acidic, slightly sweet lift that balances the richness of avocado and beans. Adding them early lets their brine perfume the cabbage.

Prepare aromatics: Warm a large skillet over medium heat with 1 tbsp olive oil (reserve 1 tbsp for the slaw). Add the finely diced onion and cook until translucent, about 4–5 minutes, stirring occasionally. Add the minced garlic and cook 30 seconds until fragrant. Why: Sweating the onion gently releases sweet, savory compounds without browning; add garlic near the end so it becomes fragrant but doesn’t burn and turn bitter.

Toast the spices: Add 1 tsp ground cumin, 1/2 tsp smoked paprika, 1/2 tsp chili powder, and 1/4 tsp red pepper flakes (or jalapeño) to the skillet and toast 20–30 seconds, stirring. Why: Toasting spices in oil 'blooms' their essential oils and deepens flavor — this step transforms ground spices from flat to aromatic.

Add black beans: Add the drained and rinsed can (or 2 cups cooked) black beans to the skillet with 1/4 tsp salt and 1/8 tsp pepper. Stir, then use a fork or a sturdy potato masher to press and partially smash about half the beans. Cook for 3–4 minutes until heated through and some beans begin to break down. Why: Partially smashing creates a mix of creamy and whole beans — a great texture for tacos that clings to the tortilla while still providing bite.

Finish the filling: Stir in 1/2 cup salsa, the juice of 1 lime (about 1 tbsp), and 1 tsp unsalted butter (optional) to enrich the filling. Taste and adjust seasoning with up to 1/2 tsp more salt if needed. Remove from heat and fold in 2 tbsp chopped cilantro. Why: A splash of salsa adds brightness and juiciness while butter smooths mouthfeel; finishing with fresh cilantro preserves its bright, herby flavor.

Warm the tortillas: Heat a second cast-iron or nonstick skillet over medium-high. Working in batches, warm tortillas 20–30 seconds per side until they’re pliable with a few charred blisters. Keep warm in a towel. Why: Heating on direct heat chars the tortilla lightly for smoky flavor and makes it flexible so it won’t tear when folded.

Assemble the tacos: Place 2 warmed corn tortillas per serving. Spoon about 1/2 cup of the black bean mixture onto each pair of tortillas (roughly 1/4 of the filling per serving). Top with a generous handful (about 3/4 cup) of the cabbage slaw, 1/4 of an avocado sliced, a spoonful of pickled onion if you like it extra bright, and 2 tbsp salsa. Why: Layering contrasts—warm, smoky beans beneath cool, crunchy slaw and creamy avocado—gives each bite complexity and balance.

Garnish and finish: Sprinkle with remaining chopped cilantro and optional crumbled cotija. Serve with lime wedges. Why: A final squeeze of lime brightens flavors, and a salty cheese (if using) adds another textural and savory note.

Serve immediately: These are best eaten right away so the tortillas remain pliable and the slaw keeps its crispness. Why: If assembled in advance, tortillas can become soggy from the filling; keep components separate for make-ahead meal prep.