Heat the olive oil in a large saucepan set over medium heat. Add the onion, carrot and celery, and cook until the vegetables are beginning to soften, about 5 minutes.
Stir in the garlic, thyme, rosemary, red pepper flakes, salt and pepper, and cook for 1 minute. Stir in the tomato paste and cook for 1 minute.
Add the cauliflower florets and vegetable broth, and bring to a boil over medium-high heat. Reduce to a simmer and cook for 5 minutes.
Increase the heat to medium-high and stir in the orzo. Cook until the pasta is almost al dente.
Stir in the kale and cook until just wilted, about 1 minute. Serve.