Preheat oven to 400 degrees F and line a rimmed baking sheet with parchment paper; coat with a nonstick spray.
In a food processor and working in batches, pulse the cauliflower until finely chopped. Transfer to a large microwave-safe bowl and toss with 2 teaspoons of salt and ½ teaspoon pepper. Cover with plastic wrap and microwave on high until tender, about 5 minutes. Remove the bowl from the microwave and let the cauliflower steam, covered, for 5 minutes.
Line a colander with a clean kitchen towel and transfer the cauliflower to the towel. Let cool slightly, then gather the towel and squeeze the cauliflower until dry. You will have about 4 cups.
Return the cauliflower to the bowl and mix with the almond flour, eggs, and parmesan. The dough should clump easily.
In a separate small bowl, mix 1 tablespoon of olive oil with the garlic. Scrape the cauliflower mixture onto the prepared baking sheet and press into a 12-by-9-inch rectangle, about ½-inch thick. Bake the crust for 20 minutes. Remove the crust from the oven and brush all over with the garlic oil.
Return the crust to the oven and bake for about 10 minutes more, or until golden brown and crisp. Carefully slide the crust and the parchment paper onto a rack and let cool slightly.
In a separate large bowl, whisk the lemon juice with the remaining 2 tablespoons of olive oil. Season with salt and pepper. Add the greens, fennel, radishes, carrot, beet, and olives and toss to coat. Season with salt and pepper.
To serve, transfer the crust to a platter or cutting board and top with the salad. Cut into squares and garnish with the fennel fronds and chives.