Cook pasta according to package directions. Drain, rinse under cold water, and set aside.

Preheat grill or grill pan over medium-high heat.

Toss zucchini, squash, bell pepper, and onion in olive oil, salt, and pepper.

Grill vegetables for 4–5 minutes per side, until tender and lightly charred. Remove from grill and chop into bite-sized pieces.

In a small bowl, whisk together olive oil, balsamic vinegar, Dijon mustard, honey, garlic, salt, and pepper for the dressing.

In a large bowl, combine cooked pasta, grilled vegetables, chopped basil, and feta cheese (if using). Drizzle with dressing and toss gently to combine.

Serve chilled or at room temperature.