In a large bowl, combine shrimp, imitation crab, onion, jalapeños, cilantro, and tomatoes.
Squeeze the juice of 2-3 limes over the mixture.
Season with salt, pepper, garlic powder, and onion powder. Start with ½ teaspoon of each seasoning, then taste and adjust as needed.
If using avocado, serve it on the side to avoid it getting mushy if the ceviche is not eaten in one sitting.
Serve immediately, or let sit in the refrigerator for a couple of hours to allow flavors to meld.
Enjoy your ceviche with tostadas or chips, and add mayo, Tapatio, or ketchup as desired.