In a large airtight container, place chicken tenders. Combine olive oil, basil, salt, and pepper and pour over chicken. Cover and refrigerate until ready to grill.
Over medium-high heat, heat olive oil in a large sauce pan for 1 to 2 minutes. Add onion and garlic. Cook until slightly tender for about 2 to 3 minutes.
Add chicken broth and black pepper. Bring to a boil.
Add quinoa to boiling broth. Cover and reduce to low-medium heat. Simmer until liquid is absorbed and quinoa is cooked and tender (about 15-20 minutes).
While quinoa is cooking, prepare avocado and tomatoes. Once quinoa is cooked, remove pan from heat and fold in avocado and tomatoes.
Grill chicken tenders over medium heat until center no longer pink (about 3 to 4 minutes). In order to keep chicken juicy, remove chicken from heat as soon as the center is no longer pink and place on a large sheet of aluminum foil. Wrap aluminum foil around chicken tenders until completely covered. Allow chicken to finishing fully cooking in the aluminum foil for about 5 more minutes.
Serve quinoa and chicken tenders together.