It's dinner time!

Ingredients

• 2 tablespoons extra-virgin olive oil
• 1 onion, thinly sliced
• 1 teaspoon kosher salt
• ½ teaspoon red pepper flakes
• ½ teaspoon ground black pepper
• 2 cloves garlic, chopped
• 1 (15 ounce) can black beans, drained
• 1 (10 ounce) can diced tomatoes with green chile peppers
• 1 (10 ounce) bag fresh baby spinach