Heat a large oven-safe skillet over medium heat and add 1 tablespoon of olive oil. Working in batches, place cauliflower in the pan in a single layer. Cover and cook for 4 to 5 minutes undisturbed. Uncover and continue cooking, stirring occasionally, until the florets are golden brown and tender, another 4 to 6 minutes. Repeat with more olive oil and remaining cauliflower. (Alternatively, roast cauliflower on a sheet pan at 400°F for 20 minutes.) Remove from the pan. Add the remaining olive oil and kale to the pan and cook, stirring occasionally, until wilted and tender, 3 to 4 minutes. Remove from the pan. Add the butter to the pan, and once it’s melted, add the garlic and stir constantly for 30 seconds, then add the flour. Whisk the mixture constantly for 1 to 2 minutes to cook the flour, then slowly add in the half-and-half, whisking all the while. Continue whisking frequently until the mixture comes to a boil, then reduce the heat and let simmer, stirring frequently, for 2 to 3 minutes, or until slightly thickened. Stir in the salt, red pepper flakes, Parmesan, parsley, lemon zest, lemon juice, and one-quarter of the feta. Heat the oven to 375°F. Add the cauliflower, kale, and cooked pasta to the pan with the sauce and toss to coat. Add ¼ cup of pasta water and stir well. Top with the remaining feta, and generously grate Parmesan over the top. Cover and bake for 15 to 20 minutes, or until bubbling, then uncover and broil for 2 to 3 minutes until the top is golden brown. Serve immediately.