This is something I actually make quite often to accompany other foods on the grill. You can use whatever you have on hand. Here I used some portobello mushrooms, onions and grape tomatoes I got today from McGinnis Sisters.
The recipe is always the same. Heat a cast iron skillet over medium high heat. I like to do it outside on the burner of the grill. Add some olive oil and butter and saute your onions until translucent and almost starting to brown. Remember to season with salt and pepper while cooking. I also added some hot peppers for flavor and spice. I usually go overboard with them, but these were extremely mild and I add 6. I think fennel would have also been a good choice. Add some garlic and other vegetables like mushrooms and tomatoes and zucchini. Saute until everything is cooked, but don’t over cook or everything will turn to mush. Add additional spices to taste. This is the important step. Without salt and pepper, your vegetables will be pretty flavorless. So be creative and find some spices you like. I often you an Italian spice mix or just some tarragon and parsley. Be careful to to burn your garlic.
Serve along side of your steak or hamburger.