1. In a skillet, heat the olive oil over medium heat. Add the chopped onion and garlic, and sauté until fragrant and translucent, about 3-4 minutes.
2. Transfer the sautéed onions and garlic to the slow cooker. Add the Arborio rice, chicken broth, white wine, saffron threads, smoked paprika, red pepper flakes (if using), diced tomatoes, and a pinch of salt and pepper. Stir to combine.
3. Cover the slow cooker and cook on low for 2 1/2 to 3 hours, until the rice is tender and has absorbed most of the liquid.
4. About 30 minutes before the rice is done, add the shrimp, peas, and red bell pepper to the slow cooker. Stir gently to distribute the ingredients evenly.
5. Cover and continue to cook on low for the remaining 30 minutes, or until the shrimp are cooked through and the vegetables are tender.
6. Before serving, taste and adjust the seasoning with additional salt and pepper if needed.
7. Serve the paella straight from the slow cooker, garnished with fresh parsley and lemon wedges on the side.
