First, make the spread.
Place all Sun-Dried Tomato Basil Spread into a food processor. Pulse until thoroughly blended but still slightly chunky. Scrape the spread into a small bowl, cover, and refrigerate until you're ready to assemble the burgers.
Prepare your grill or grill pan by heating it to medium-high and coating it with cooking spray.
Prepare the mushrooms. Lightly spray the gill side of the mushroom caps with cooking spray and season with a pinch of salt and pepper.
Place the mushrooms gill-side down on the hot grill and cook for 5 minutes.
While the first side cooks, spray the tops of the mushrooms with cooking spray and season with more salt and pepper.
Flip the mushrooms. Gently place a heavy, heat-proof pan (like a cast-iron skillet) on top of the mushrooms to press them down slightly.
Cook until tender, about 3-5 more minutes.
Build your burgers! Generously slather the Sun-Dried Tomato Basil Spread on both the top and bottom toasted buns. On the bottom bun, layer a handful of arugula, a grilled mushroom cap, and a few tomato slices.
Place the top bun on and serve immediately.
Marinate the mushrooms for 30 minutes before grilling in a mix of balsamic vinegar, olive oil, and garlic for an extra flavor boost.
Add a slice of provolone or Swiss cheese on top of the mushrooms during the last minute of grilling and let it melt for a gooey, delicious finish.