Using a box grater, finely grate the zucchinis until they resemble a pulp, then set aside.
Heat olive oil in a large skillet over medium heat until it shimmers and starts to gently bubble.
Add the grated zucchini to the skillet and cook, stirring often, for about 5-7 minutes until it releases a fresh aroma and softens slightly.
Push the zucchini to one side of the pan and add the chopped onion and minced garlic to the cleared space, sautéing until the onion becomes translucent and fragrant, about 3-4 minutes.
Pour in the crushed tomatoes, stirring everything together, then bring the mixture to a gentle simmer.
Let the sauce simmer uncovered for 15-20 minutes, stirring occasionally, until it thickens slightly and the flavors meld.
Stir in red pepper flakes and season with salt and pepper to taste, adjusting for your preferred spice level and saltiness.
Remove the skillet from heat and fold in the chopped fresh basil, allowing its aroma to infuse the sauce.
Serve the zucchini bolognese hot over your favorite pasta or zucchini noodles, garnished with extra basil if desired.