Preheat your Ninja Foodi Grill by selecting the GRILL setting and setting the temperature to medium.
While the grill is preheating, wash the zucchinis and cut off the ends. Slice the zucchinis lengthwise into 1/4 inch thick strips.
Brush the zucchini slices with olive oil on both sides. Then sprinkle with salt, pepper, and any additional herbs or spices if you're using them.
Once the grill is preheated, arrange the zucchini slices on the grill plate. Close the grill and let the zucchini cook for about 3-4 minutes.
Open the grill and flip the zucchini slices over. Close the grill again and let the other side cook for another 3-4 minutes.
Check the zucchini for doneness. The slices should be tender and have nice grill marks. If they're not done to your liking, you can continue grilling for another 1-2 minutes.
Once the zucchini is done, carefully remove it from the grill using a spatula. If desired, sprinkle with grated Parmesan cheese while the zucchini is still hot.
Let the grilled zucchini cool for a few minutes before serving.