Skewer the mushrooms, onions and bell peppers. It’s best to not mix vegetables on the skewers as you may find they need slightly different cooking times. Place the skewers on a large baking sheet.
Combine the olive oil, cilantro, jalapeño, garlic and lime juice in a mixing bowl. Use a grill brush to brush the mixture onto the skewers on both sides, and finish with a pinch of salt and pepper. Refrigerate the vegetables for 20 minutes.
While the vegetables are marinating, heat a grill or grill pan up to high heat. Brush the grill or grill pan with canola oil and place all of the skewers in a single layer. Grill for 5 minutes, until the vegetables have begun to char, and flip and repeat for another five minutes.
Use tongs to remove the skewers from the grill and slide the vegetables off the skewers onto a serving platter.
Assemble the tacos starting with the grilled vegetables, followed by the corn, avocado, crema and squeeze of lime.