PREHEAT oven to 400F. Line a large rimmed baking sheet with foil. Spray with oil. Set aside.
SLICE eggplants lengthwise into 1/4-in.- thick slices. There will be about 16 slices. Discard outside slices or keep for another use. Lightly brush both sides of eggplant slices with about 2 tbsp olive oil. Lay on prepared baking sheet and bake in centre of oven until edges are fork-tender, about 15 min. Set aside to cool.
HEAT a large non-stick frying pan over medium. Add 1 tsp oil, then onion, garlic and 1/2 tsp salt. Cook until onion is soft, 3 min. Stir in ricotta, parmesan, lemon zest and 1/4 cup basil. Stir until heated through, about 2 min. Season with fresh pepper. Transfer mixture into a medium bowl. Set aside.
RETURN pan to heat and increase to medium-high. Add remaining oil, tomatoes and remaining salt. Bring to a boil, then reduce heat to medium. Simmer, uncovered, stirring occasionally, until saucy, about 20 min. Remove from heat and stir in remaining basil. Season with fresh pepper. Keep warm.
SPOON 2 tbsp ricotta mixture onto 1 end of each eggplant slice. Gently roll up. Place involtini on a large warmed serving platter, seam-side down. Repeat with remaining eggplant and ricotta mixture. Top with half of tomato sauce. Serve immediately with remaining tomato sauce alongside.