Preheat the oven to 450 degrees. Drizzle 2 tablespoons of the olive oil into a 9–by-13 inch baking dish and use your hand to evenly coat the entire surface. Set aside.
Heat the remaining 2 tablespoons olive oil in a large frying pan over medium-high heat.
Add the onions, 1-teaspoon salt and the thyme. Lower the heat to medium and cook, stirring frequently, until the onions are soft and nicely browned, 10 to 15 minutes.
Transfer to a bowl and place in refrigerator to cool completely.
Combine cooled onion mixture with remaining ingredients in a large mixing bowl and mix by hand until thoroughly incorporated.
Roll the mixture into round, gold ball-sized meatballs (about 1.5 inches), making sure to pack the meat firmly. Place the balls in the prepared baking dish, being careful to line them up snugly and in even rows vertically and horizontally to form a grid. The meatballs should be touching one another.
Roast for 20 minutes, or until meatballs are firm and cooked through. A meat thermometer inserted into the center of the meatballs should read 165 degrees.
Allow meatballs to cool for 5 minutes in the baking dish before serving.