Preheat your oven to 400°F (200°C). Wrap the two heads of garlic in aluminum foil, making sure they’re tightly sealed. Roast in the oven for about 30-35 minutes, or until the cloves are soft and golden brown.
While the garlic is roasting, chop the cauliflower into florets. Toss the florets with 2 tablespoons of olive oil, a pinch of sea salt, and black pepper. Spread them out on a baking sheet and sprinkle with fresh thyme leaves. Roast in the oven for about 25-30 minutes until tender and caramelized.
In a large pot of boiling salted water, cook the short brown rice pasta according to package instructions until al dente. Reserve about 1 cup of pasta water, then drain the pasta and set aside.
Once the garlic and cauliflower are done roasting, let them cool slightly. Squeeze the roasted garlic cloves out of their skins into a food processor. Add the roasted cauliflower, lemon juice, red pepper flakes, and remaining olive oil. Blend until smooth, adding reserved pasta water as needed to reach your desired consistency.
In a large mixing bowl, combine the cooked pasta with the roasted garlic and cauliflower sauce. Toss well to coat. Add the arugula and toasted walnuts, mixing gently. Adjust seasoning with more salt, pepper, and lemon juice if desired. Serve warm, garnished with extra walnuts and a squeeze of lemon juice.
