Heat olive oil in a large sauté pan over medium-high heat until shimmering but not smoking. Pat the chuck roast dry with paper towels, then season liberally on all sides with Kosher salt and freshly cracked black pepper.
Carefully add the seasoned roast to the hot pan, searing on all sides including edges, which should take about 4-5 minutes per side until browned deeply but not cooked through.
Once seared, remove the roast from the pan and set aside in your slow cooker. Without cleaning out the pan, reduce heat to medium, add sliced onions with a couple of pinches of salt and pepper, cooking while stirring occasionally until softened, about 4 minutes.
Stir in smashed garlic cloves along with tomato paste, brown sugar, Italian seasoning, garlic powder, onion powder, chili powder, and additional salt and pepper; cook this mixture for another minute until fragrant.