First, cook the pasta. Bring a large Dutch oven full of salted water to a boil. Add pasta and cook until al dente. Set aside 2 cups of pasta water for later. Strain and rinse the noodles with water. Set aside.
Add 2 tablespoons of the pasta water to the Dutch oven and add the spinach. Heat over medium heat and cover until the spinach is wilted. Strain excess water and transfer the spinach into a mixing bowl.
Prepare the meatballs. Add 3 tablespoons of olive oil, egg, garlic, breadcrumbs, Italian seasoning, salt, and parsley to the spinach and mix until just combined with a spatula or hands. Do not overmix, it will cause the meatballs to be tough.
Wet your hands and use a tablespoon and scoop a heaping tablespoon of the meat mixture into your hands and roll the meat into a ball. Transfer it to a plate. Repeat until all the mixture has been made into meatballs.
Heat the remaining olive oil in the Dutch oven over medium/high heat. When the olive oil is fragrant, add the meatballs. Cook the meatballs for 1-2 minutes on each side until browned. Use tongs to gently move the meatballs so they don’t stick to the Dutch oven during the cooking time. This will take about 6 minutes. The meatballs will not be fully cooked. They will continue to cook in the sauce. Remove the meatballs from the pot.
Turn the heat to medium and deglaze the pot with white wine. Scrape the brown bits from the bottom of the pot with a spatula.
Heat the olive oil in the pot with the wine over medium/high heat. Add the onion and season with ¼ teaspoon of salt. Saute for 3-4 minutes. Add the garlic and saute for an additional 1 minute or until fragrant.
Add the green pepper and sauté for 2-3 minutes, and add the tomato paste and 1.5 cups of starchy pasta water* to the pot. Whisk the tomato paste into the starchy water.
Transfer the meatballs, remaining salt, and pepper to the pot and bring the sauce to a simmer over medium/high heat.
Then, turn the heat to medium/low and simmer until it thickens to the desired consistency. If you would like a thinner sauce (or more sauce), add the remaining pasta water and simmer.
When the internal temperature of the meatballs is 165ºF, gently toss the pasta with the sauce and meatballs. Heat until warmed through, and enjoy.