Prepare all vegetables by washing and cutting them into bite size pieces.
In a bowl, toss bell pepper, broccoli, and carrots with 2 Tbsp olive oil, salt, pepper, and garlic powder. Set tomatoes and red onion to the side (they tend to cook much quicker).
Place grill basket on hot grill over indirect flame and allow to heat up (5 minutes or so).
Dump the prepared bell pepper, broccoli, and carrots into the grill basket stirring occasionally. You will want to watch them closely so they do not burn (but a little char adds some good flavor in my opinion).
Half way through cooking, add tomatoes, red onion, and additional 2 Tbsp of olive oil to the grill basket. Stir to combine.
Cook until desired tenderness and serve warm.