To make the marinara, put the tomatoes in a bowl and crush with your hands. Heat two tablespoons of the oil in a saucepan over medium heat. Add the onion, oregano, and a pinch of salt and chili flakes. Saute until soft and translucent, about 5 minutes. Add the garlic and cook another minute. Stir in the tomatoes. When the sauce comes up to a simmer, add the remaining oil and turn the heat to low. Continue to cook for 10-15 minutes. Adjust seasoning as needed.
Cut the chicken tenders in one-inch pieces. Toss them in a bowl with enough marinara to coat. Set aside.
Take an egg roll wrapper and lay it flat on a counter, corner pointed down toward you. Put one and a half slices of fresh mozzarella in the wrapper. Top with 3-4 pieces of the chicken. Season with salt and pepper. Starting at the closest corner to you, roll the wrapper tightly over the filling, like a burrito. Tuck in corners to form a seal. Wet a finger and rub furthest exposed wrapper corner. Continue rolling and seal with the corner that has been moistened.
Lay on a sheet tray. Sprinkle finished spring rolls with corn starch to avoid sticking together.
Heat a wide pot with 3" of canola oil to 350℉. Gently lay the rolls in the oil, a few at a time. Fry until golden. Remove with a slotted spoon and drain on a sheet tray lined with paper towels. Serve with extra marinara and grated Parmesan cheese.