Bring a pot of well-salted water to a boil. Cook pasta until al dente, according to package instructions. Drain and toss with a little bit of olive oil to prevent sticking. Set aside.
Heat 1 Tbsp. olive oil in a medium skillet over medium heat; add the onion and cook until tender, 6-8 minutes, stirring often. Remove from heat and allow to cool.
Place the cooled pasta in a large bowl. Add the drained garbanzo beans, tomatoes, cucumbers, basil, and cooled onions.
Make the light dressing:
In a small bow, mix the lemon juice and 4 Tbsp. olive oil; salt and pepper to taste. Pour over the salad mixture and gently mix together.
Sprinkle with feta cheese. Drizzle with remaining 1 Tbsp. olive oil; serve.