Heat olive oil in a saucepan over medium heat; cook and stir onion and garlic in the hot oil until slightly browned, about 5 minutes. Stir quinoa into onion mixture and cook until quinoa is lightly browned, about 30 seconds.
Squeeze lime juice into a 2-cup measuring cup; pour in enough chicken stock to make 2 cups liquid. Pour chicken stock mixture over quinoa and bring to a boil. Reduce heat, cover saucepan, and simmer until liquid is absorbed and quinoa is tender, about 15 minutes. Remove saucepan from heat and chill in the refrigerator, about 1 hour.
Fold cilantro, tomatoes, avocado, and jalapeno pepper into quinoa mixture. Return quinoa to refrigerator for flavors to blend or serve immediately.