Cut the shrimp and tilapia into 1” pieces and place them in the bowl of the food processor. Add the remaining ingredients except the chicken stock. Pulse to chop the fish and combine everything. Don't puree the fish completely, stop short of that. With wet hands, form the mixture into 12 balls.
Bring the chicken stock to a boil. Carefully drop in the fish balls. When the stock comes back to a simmer, turn the balls, cover the pan and let it sit for 5-6 more minutes before serving with rice, orzo, or some other favorite thing of yours.