Preheat oven to 350°F. Place the walnuts on a baking tray in a single layer and toast for 7-10 minutes. Walnuts are finished when they appear a shade darker and smell toasty. Cool completely.
Preheat oven to 400°F. Place the cauliflower florets in a food processor and pulse until it resembles rice but is still coarse. You should have about 6 cups. Mix cauliflower with 3 tbsp of olive oil. Divide cauliflower between two baking trays in a single layer and roast for 20-25 minutes until softened and golden, tossing halfway through.
Meanwhile, clean your food processor and begin the pesto. Add the sun-dried tomatoes, capers, garlic, walnuts, basil leaves, lemon juice, and olive oil. Pulse until a coarse paste.
Combine the cauliflower, pesto mixture, and currants. Enjoy warm!