Make the filling: Heat 1tbsp oil in a skillet, add the onion, garlic and jalapeno. Saute till onions are translucent.
Next add the black beans and spinach and cook till spinach is wilted and cooked through, about 3~5 minutes.
Add the chili powder, ground cumin, salt and pepper. Mix well and cook for 2 more minutes.
Make the Sinchronizadas: Lightly grease a nonstick skillet and heat over a medium heat
Place one tortilla on the pan and top it with a layer of filling and cheese. Generously spread salsa over the other tortilla and place it salsa-side down on top of the cheese and filling tortilla in the pan.
Cook until cheese is melted and the base of the tortilla is golden brown.
Carefully flip the sincronizada by placing a heatproof plate, upside down, on top of the pan. Taking care to protect your hands, hold the plate firmly in place and carefully invert the pan onto a plate.
Slide it back into the pan and cook till the other side of the tortilla is golden brown.
Remove from the pan and cut into wedges. Repeat with the remaining filling and tortillas. Serve with sour cream.