If you like your food spicy, you can add a diced jalapeño or serrano pepper to the slow cooker along with the other ingredients. You can also top your tacos with hot sauce or additional sliced peppers. However, the spiciness level will depend on what kind of taco seasoning and salsa you use in this slow cooker chicken tacos recipe. Look for hot, medium, or mild seasonings and salsas depending on your preference.