Preheat grill to medium-high heat. (If using charcoal, wait for charcoal to turn ash-colored. Target temperature is ~400°F.)

Using a small bowl, combine garlic, thyme, salt and pepper. Press mixture evenly into both sides of steaks; set steaks aside.

Brush mushrooms with olive oil.

Place steaks and mushrooms on grill. Cover and grill for 3-4 minutes. Flip and continue grilling for 6-10 more minutes, depending on desired doneness of steaks. Remove steaks from grill and set aside to rest for at least 5 minutes. Continue grilling mushrooms, turning occasionally, for another 5-10 minutes (i.e. 14-18 minutes total for mushrooms), or until tender.

Combine all ingredients (blue cheese, butter, sundried tomatoes and parsley) together in a small bowl.

Spread 1-2 Tbsp of Blue Cheese Butter on top half of each slider bun; set buns aside.

After steaks have rested for at least 5 minutes, slice as thinly as possible.

Divide spinach among the bottom halves of the slider buns and then top with sliced steak. Top each slider with a grilled mushroom and top half of bun.