Bring a medium [large] sauce pot of generously salted water to a boil. Separate the penne so the noodles don’t clump together during cooking. Add the penne and cook, stirring occasionally, until just tender, 3 to 5 minutes. Drain the penne, reserving ¼ cup [½ cup] pasta cooking water. Transfer the penne to a medium bowl; toss with 1 to 2 teaspoons oil to keep the noodles from sticking. Wipe the pot dry.
While the water heats and the penne cooks, prepare the meatballs.

• Cut a small corner from the ground turkey packaging and drain off any excess liquid. Transfer to a plate; pat dry with a paper towel.
• Strip the parsley leaves from the stems; coarsely chop the leaves. Set aside half for garnish.

In a medium bowl, combine the turkey, meatball spice blend, and half the parsley. Season generously with salt and pepper and mix until just combined. Using wet hands, form the mixture into 1-inch meatballs.

In a large frying pan over medium-high heat, warm 1 to 2 teaspoons oil until hot but not smoking. Add the meatballs and cook, turning once, until lightly browned but not yet cooked through, 2 to 3 minutes per side. Transfer to a plate.

In the same pot used for the penne, warm 1 to 2 teaspoons oil over medium-high heat until hot but not smoking. Stir in the mirepoix, season with salt and pepper, and cook until starting to soften, 1 to 2 minutes. Add the meatballs, herbed marinara, and reserved pasta cooking water and bring to a boil. Reduce to a simmer, cover, and cook until the meatballs are cooked through, 5 to 7 minutes.
Working in batches if needed, stir in the spinach and cook until just wilted, 1 to 2 minutes. Stir in the penne and cook until warmed through, 1 to 2 minutes. Remove from the heat and season to taste with salt and pepper.

Transfer the penne and meatballs to individual bowls, garnish with the remaining parsley, and serve.