Place the cauliflower florets in a large pot and cover with water so they are submerged; bring to a boil.
Reduce heat to low, cover, and simmer until the cauliflower is very soft, about 22 minutes; drain and let cool slightly.
Working in batches, place warm cauliflower in a clean dish towel or cheesecloth and squeeze out as much water as possible, then transfer to a large bowl.
Add the flour and kosher salt to the drained cauliflower and mix with a fork, then use your hands to fold and squeeze into a cohesive dough.
Lightly dust a work surface with flour and divide the dough into 8 equal pieces (about 2½ ounces each). Roll each piece into a ½-inch-thick rope about 10 inches long.
Cut each rope into approximately 13 pieces to make gnocchi (about 108 pieces total). If the dough sticks, dust hands with more flour.
Heat a large skillet over medium and generously mist with olive oil spray. Working in two batches, add half the gnocchi without overcrowding the pan.
Cook the gnocchi undisturbed for 2 minutes, then gently flip with a spatula or tongs and sprinkle with a little salt; cook another 2–4 minutes until browned and cooked through.
Repeat with the remaining gnocchi, return all gnocchi to the skillet, pour the marinara over them, stir to combine, and serve topped with optional grated Parmesan and basil.