Add olive oil to marinating bowl with lid, for instance tupperware. Add Italian seasoning and basil and stir.
Cut ends off cloves of garlic and remove outer flaky layer. Slice the cloves into circles, then cut the circles in quarters. Add to oil mixture and stir.
Slice red and green peppers open lengthwise. Cut out stem and remove. Remove seeds from inside with butter knife and rinse in sink. Slice lengthwise into long strips about 1 1/2" wide. Place into olive oil mixture.
Cut ends off onion. Cut onion into 8ths and then break layers apart. Place into olive oil mixture and mix with the peppers. Make sure each piece is coated well. Disposable gloves are good for this!
Marinate for at least an hour. If you have time, cover and marinate for a day or two, going in and turning the onions and peppers in the oil a couple of times a day to make sure that they remain coated.
Heat George Foreman grill to medium. Put peppers on only, evenly across grill marks. Since the peppers are curved near the top and bottom of each strip, you will have to straighten them out. Close the cover and cook 2-3 minutes. Reposition them to make sure they are straightened out once the edges are no longer curled.
Add onions and garlic pieces. Cook 3-4 min, then turn grill to high. Cook 3-4 more minutes.
Now put peppers going the opposite way, so that grill marks will have a square pattern. Turn onion mixture over to ensure even browning. Cook about 8 minutes more, checking halfway through to make sure the peppers and onions are not getting too burnt.
Remove from heat. Each vegetable can be served separately, or mixed together. Buon appetito!