Step 1

Slice the tomatoes in half crosswise and gently squeeze the seeds into a bowl. Reserve 1 tablespoon of the liquid from the bowl of seeds and discard the rest. Grate the tomatoes on the coarse side of a box grater set over a bowl, pressing the cut side of the tomato against the grates. Discard the skins.

Step 2

Use the same box grater to grate the onion into another medium bowl until you have about 2 tablespoons. (Keep the remaining onion for another use.) Place the oats and the reserved tomato liquid into the bowl, stir and let sit until the liquid is absorbed, 1 to 2 minutes. Mince one of the garlic cloves and add it to the bowl along with the egg, 2 tablespoons of the parsley, and 1/4 teaspoon each of the salt and pepper, and stir to combine. Add the turkey and mix with your hands to combine, but avoid overmixing.

Step 3

Form the turkey mixture into 12 balls, wetting your hands with cold water if they become sticky as you work. If the meatballs seem loose, refrigerate them for 30 minutes to firm them up.

Step 4

Thinly slice the remaining garlic clove. In a large, deep skillet over medium-high heat, heat 2 tablespoons of the oil until shimmering. Add the meatballs and cook, turning them two to three times, until browned all over and nearly cooked through, about 5 minutes.

Step 5

Stir the remaining 1 tablespoon of oil, the harissa, the sliced garlic, the remaining 1/8 teaspoon salt and 1/4 teaspoon pepper into the bowl of tomatoes, then pour the tomatoes into the skillet with the meatballs. Reduce the heat to medium and bring the sauce to a boil, then cook, uncovered, stirring occasionally, until the meatballs are cooked through and the sauce has somewhat thickened, about 10 minutes. Taste and add more harissa, if desired.

Step 6

Divide the meatballs and sauce among 4 bowls, garnish with the remaining parsley, and serve with crusty bread or over couscous.