Preheat the oven to 400 degrees F.
In a small food processor, pulse the oats until coarsely ground. Add to a large mixing bowl.
To the same bowl, add the egg, tomato paste, basil or mint, garlic, shallot, paprika, and salt. Mix with a fork until the ingredients are well distributed.
With clean hands, mix the ground beef with the other ingredients until loosely combined. You don’t want to overly break up the meat. Form the beef into a dozen 2-inch balls (an ice cream scoop works well for portioning) and roll in your hands until round and smooth. Arrange the balls on a parchment-lined baking sheet and bake in the oven until cooked through and beginning to brown on the bottom, about 20 minutes.
While the beef meatballs are baking, make the sauce: in a large saucepan, heat the oil over low heat. Add the garlic and cook until golden, about 2 minutes. Off the heat, carefully add the harissa and cook for one minute more, until you have a fragrant chili garlic oil. Stir in the tomato or marinara sauce and half the basil or mint. Simmer over medium-low heat, stirring occasionally, until heated through a beginning to reduce, about 3 minutes.
Toss the baked beef meatballs with the harissa sauce and garnish with the remaining herbs. Serve immediately over pasta or on their own!