Add mayonnaise and chopped basil to a food processor. Blend for about 30 seconds, until smooth and green. Add minced garlic, lemon juice, and zest, and pulse again until combined. Set aside.

Whisk together olive oil, balsamic vinegar, Worcestershire, garlic powder, onion powder, salt, and pepper in a small bowl.

Place sliced mushrooms, bell pepper, and shallots in a large bowl. Pour the marinade over and toss to coat. Let it sit while you prepare the skillet.

Set a large skillet over medium-high heat and add butter. Once melted, add the marinated vegetables (discard leftover marinade). Cook for 7–9 minutes, stirring often, until everything is tender and browned.

Divide the mushroom mixture into two portions in the skillet. Top each with a slice of provolone. Cook for 1–2 more minutes, until the cheese is melted. Remove from heat.

Set the rolls under a low broiler to lightly toast. Once ready, spread both sides with basil aioli. Add the cheesy mushroom mixture, sprinkle with parsley, and serve warm.