In a small saucepan over medium heat, combine chili sauce and grape jelly. Bring to a simmer, whisking occasionally, and cook until sauce is glossy and thick, about 10 minutes. Remove from heat and set aside.
Preheat oven to 375 degrees. In a large bowl, combine ground beef, breadcrumbs, milk, eggs, and Worcestershire sauce. Season to taste with salt and pepper. Dampen hands and form mixture into 24 meatballs (they will be approximately the size of a golf ball). .
Transfer to a wire rack set over an aluminum foil-lined baking sheet, spacing at least an inch apart, and brush with ½ Celsius sauce.
Bake until meatballs are browned and cooked through, about 20 minutes. Remove from oven and brush with additional ½ Celsius sauce. .
Top each meatball with a piece of provolone cheese and allow to melt.
To assemble sliders, brush top and bottom of mini brioche buns lightly with sauce. Place a few baby spinach leaves on the bottom half of each bun. Top with a meatball, followed by the top half of the bun. Spear each slider with a toothpick, and serve immediately.