Preheat the oven to 200 degrees. Slice the zucchinis lengthwise into three-millimeter slices, preferably using a mandoline. Sprinkle them lightly with salt and let them sit on paper towels for ten minutes. This draws out moisture, which is exactly what you want: dry slices get a real crust on the grill, whereas wet slices only steam and remain soggy.
Heat a grill pan, brush the slices with a tablespoon of olive oil, and grill them for one and a half minutes per side until pliable and marked with dark grill lines. Let them cool on a plate.
Heat a tablespoon of olive oil in a pan, sauté a finely chopped clove of garlic for half a minute, and stir in the spinach until wilted. Let it cool and squeeze out as much moisture as possible.
Meng the ricotta with the spinach, half of the grated Parmesan, lemon zest, salt, and black pepper.
Heat the remaining olive oil in a small saucepan, sauté the second clove of garlic with the oregano, and pour in the passata. Let the sauce simmer and reduce for fifteen minutes until thick, then season to taste.
Spoon a dollop of filling onto each zucchini slice, roll them up, and place them upright in a baking dish on top of the sauce. Sprinkle with the remaining Parmesan and bake for twenty minutes. Finish with toasted pine nuts and basil.