Thaw burgers in refrigerator overnight.
Split the 4 burger patties in half and form 8 slider-sized burger patties about 1” thick.
Pat dry with paper towel on all sides, generously season on all sides with blackened seasoning, and allow to sit at room temperature for 10 minutes.
In a large cast-iron pan, add grapeseed oil and bring to medium-high heat.
Add 4 sliders to pan and cook 3 minutes on one side, flip, and continue to cook until desired doneness as per a meat thermometer; repeat process for remaining 4 sliders.
Bring a separate large pan to medium-high heat.
Spread 1/2 tablespoon mayonnaise on each half of slider buns and toast in pan about 30 to 45 seconds, until buns are golden brown.
Assembly: Place slider on bottom bun, crisscross 2 halved bacon slices and add a heaping spoonful of cheese sauce, about a tablespoon of bleu cheese crumbles, and a small handful of crispy onion straws and top with top bun.