In a heavy saucepan over medium-high heat, fry pork and onions until onions become light brown, about 10 minutes. Add tomatoes and peppers; simmer on low 2 hours. Add potatoes and corn; cook until tender, about 10 minutes. In a large stockpot, bring 1 quart of water to boil. Add mussels and steam until shells open (discard any that do not open). When shells open, transfer mussels to a colander, saving any liquid. Strain liquid and add to pot with vegetables. (If desired, remove mussels from their shells; discard shells and reserve mussels.) Season vegetables (be sure to taste first – the mussel broth will be naturally salty) with salt, pepper, cayenne, and paprika. Add mussels to pot just before serving.