Cook quinoa according to package directions. Drain and set aside to cool.
Cube avocados, and then cut tomatoes into quarters. Set aside.
In a small bowl, combine lemon juice, olive oil, garlic, salt, and pepper. Stir and set aside.
In a large serving bowl, add avocadoes, tomatoes, and cooled quinoa. Pour in the dressing and toss everything together. Taste, and add additonal salt if necessary.