Heat olive oil in a large Dutch oven or heavy pot over medium heat. Add the chorizo slices and cook until they release their oils and start to crisp, about 5 minutes. Remove and set aside.
In the same pot with the chorizo drippings, add the onion and bell pepper. Sauté until softened, about 5-6 minutes.
Add the garlic, smoked paprika, cumin, and red pepper flakes (if using). Cook for 1 minute until fragrant.
Add the cubed potatoes and stir to coat with the spices.
Pour in the diced tomatoes and chicken broth. Return the chorizo to the pot and stir everything together.
Bring to a boil, then reduce heat to medium-low and simmer uncovered for 25-30 minutes, until potatoes are tender.
Stir in the white beans and spinach. Cook for another 5 minutes until the greens are wilted and beans are heated through.
Season with salt and pepper to taste. The stew should be thick and hearty—if it's too thin, simmer a bit longer; if too thick, add a splash more broth.
Let the stew rest for 10 minutes before serving (or refrigerate overnight for maximum flavor). Garnish with fresh parsley and serve with crusty bread for dipping.