- Heat a medium pot of water over medium heat until boiling. Add potatoes and parboil 6-8 minutes, until tender but still firm.
- While potatoes cook, combine ingredients for dressing in a food processor and pulse until smooth. Transfer to a jar and set aside.
- Drain potatoes and transfer to a plate or baking sheet. Thread mushrooms on skewers and place on baking sheet. Add bell peppers, asparagus, red onion. Brush vegetables liberally with olive oil and season with salt and pepper.
- Heat a large grill pan or outdoor grill over medium-high heat (about 400ºF-450ºF) and grease with cooking oil. Place vegetables on grill and cook for 3 minutes on each side.
- Transfer grilled vegetables to a cutting board and cool for 5 minutes. Slice large vegetables into small pieces and arrange on serving plate.
- Top with pesto dressing and gently toss to coat. Serve warm. Salad can also be refrigerated for 1 hour and served chilled.