In a large frying pan, heat 2 tablespoons of the oil over medium heat. Add the onion and cook, stirring, until golden, 8 to 9 minutes. Add the garlic and cook for 1 additional minute.
Add in the black beans and the chili powder, oregano, cayenne, ½ teaspoon salt and ¼ teaspoon black pepper and cook for 3 additional minutes. Add more salt and pepper to taste.
Scatter the chips on a large rimmed baking sheet.
Scatter the onion-bean mixture on top of the chips.
Bake until the cheese is melted and bubbling about 15 minutes. Remove from the oven and scatter with the remaining jalapeños, the tomato and green onions. Serve right away.