Preheat your grill to medium-high heat, approximately 400°F. Allow the grates to heat for five minutes while you prepare vegetables. This ensures proper charring and prevents sticking throughout cooking.
Combine butter, olive oil, minced garlic, salt, black pepper, garlic powder, and red pepper flakes in a small bowl. Mix thoroughly until the garlic distributes evenly throughout the butter mixture. Set aside near your grilling station for easy access.
Brush all vegetable pieces generously with your butter mixture on both sides. Work systematically through zucchini, squash, asparagus, peppers, and mushrooms until completely coated. Reserve any remaining butter mixture for basting during cooking.
Place larger vegetables (zucchini, squash, peppers) directly on oiled grill grates first, as they require more time. Grill for 6-8 minutes per side until deep char marks develop. The charred buttery labor day grilled veggies recipe achieves perfect texture when you resist moving them frequently.
Add asparagus and mushrooms to the grill after six minutes. These smaller pieces cook faster—typically 4-5 minutes per side until tender with charred edges.
Baste all vegetables with reserved butter mixture every two minutes for maximum flavor absorption. Watch for dripping butter, which may cause flare-ups near flame areas.
Transfer finished vegetables to a serving platter as they complete cooking. Scatter fresh parsley and thyme over the top while still warm. Squeeze fresh lemon juice across everything just before serving for brightness.