Heat oil over medium-high heat in a sauté pan. Add onions and oregano, and cook until the onions are translucent and turning brown, about 5 minutes. Add in the cumin and cayenne and cook for 1 minute.
Add the black beans and cook for 3 minutes. Remove from heat and puree the mixture until desired smoothness is reached. Add in water or bean broth a teaspoon at a time if the dip is too stiff. Stir in salt and lime juice. Adjust for seasoning and serve warm or at room temperature with Baked Tortilla Chips.