Light the grill and brush some oil over a grilling tray.
Cut the lettuce heads in half. Brush with oil and sprinkle with seasoned salt, and coarse ground pepper.
Place the onion, mushrooms, snow peas, carrots and garlic in a sealable plastic bag (or bowl with a lid). Add oil and vinegar to the bag, seal the bag, and shake to coat the vegetables thoroughly.
Place the lettuce heads cut side down on the grilling tray. add the veggies to the tray.
Place on the grill. Grill for 10 - 15 minutes. The amount of time it takes will depend on the heat of your grill.
While your veggies are grilling, combine vinegar, oil, mustard, garlic powder, salt, and pepper in a lidded cruet. Shake to combine the ingredients.
Place the lettuce heads on a plate, cover with the grilled veggies, and drizzle with balsamic vinaigrette.
Recipe by Premeditated Leftovers™ at https://premeditatedleftovers.com/?p=13900