In a large pot, heat the olive oil over medium heat. Add the diced onion and bell pepper, and sauté for about 5 minutes until softened.
Stir in the minced garlic, cumin, oregano, smoked paprika, and cayenne pepper (if using). Cook for an additional 1-2 minutes until fragrant.
Add the black beans, diced tomatoes, vegetable broth, and bay leaf to the pot. Stir well to combine.
Bring the mixture to a boil, then reduce the heat to low and let it simmer for 20-25 minutes, stirring occasionally.
Season with salt and pepper to taste. Remove the bay leaf before serving.
Stir in the chopped spinach and cook for another 2-3 minutes until wilted.
Serve hot, garnished with fresh cilantro and lime wedges on the side.