1) Beat the egg in a large mixing bowl. Add the ground turkey, Panko, 2 Tablespoons olive oil, parmesan, garlic, oregano, basil, salt, and pepper in a large bowl. Mix everything up just so the ingredients are combined - avoid overmixing. Roll into desired size balls - mine were slightly larger than a golfball. Some people prefer them larger, some prefer them smaller. Place all rolled meatballs on a large baking sheet.
2) Place onion slices in the bottom of the crockpot, topped with 1 can of crushed tomatoes.
3) Coat a large skillet with remaining Tablespoon of olive oil and bring to medium-high heat. Lightly brown the meatballs (only 6-8 meatballs at a time) for about 1 minute on each side. Do not skip this step - read above for why. Layer the meatballs into the crockpot as you're browning each batch. Once all browned meatballs have been added to the crockpot, pour remaining can of tomatoes on top.
4) Cover and cook on low for 6-6.5 hours. Serve with pasta, as meatball subs, plain, etc. No matter how I serve them, I always top with a little chopped fresh basil. Store leftovers covered tightly in the refrigerator for up to 1 week.
MAKE AHEAD/FREEZE: Prepare meatballs through the browning stage; cover and refrigerate for up to 1 day or freeze up to 2 months. Add to crockpot and cook as directed. OR you may fully prepare 1 day in advance, refrigerate, then cook in the crockpot on low for 45 minutes or until warmed. Freeze cooked meatballs in sauce for up to 2 months. Defrost before reheating as desired.
NO SLOW COOKER? No problem! Prepare through step 2. Add the shaped meatballs to a large skillet coated with 1 Tablespoon olive oil and saute until browned on all sides, about 5 minutes. Transfer back to the large baking sheet. Repeat with all meatballs since they cannot all fit into the pan at once. Turn off heat. Pour off any excess oil. In a very large pot, add the sliced onions and 1 can crushed tomatoes. Add the meatballs and pour remaining can of crushed tomatoes on top. Turn the heat to low-medium and simmer until the sauce thickens slightly, the flavors blend, and the meatballs are cooked through, 25-35 minutes.
*You need 2 lbs total ground turkey. I like to use a mix of extra extra lean and lean for best flavor, while keeping them on the lighter side.
Yield: about 25 medium-size meatballs, Prep Time: 35 minutes, Total Time: 6 hours, 35 minutes