Cut cauliflower into small florets. Whisk together olive oil with minced garlic, salt, black pepper, juice of ½ lemon, and Dijon mustard. Toss cauliflower with half of the vinaigrette, reserving the other half. Spread in an even layer on a baking sheet and roast for 25 minutes or until tender, tossing the cauliflower halfway through.
Meanwhile, make the chorizo breadcrumbs. Chop the chorizo into small chunks. Heat oil in a saute pan over medium heat. Add the chorizo and saute until browned, about 3-4 minutes. Add panko and stir to combine. Continue to cook until the breadcrumbs become golden brown. Remove from heat and drain the chorizo breadcrumbs on paper towels.
Remove the cauliflower from the oven. Preheat broiler to high.
Drizzle the remaining vinaigrette on top of the cauliflower and sprinkle grated gruyere, and grated parmesan. Broil for 3-4 minutes or until the cheese is melted and slightly browned. Sprinkle chorizo breadcrumbs on top and chopped chives. Serve immediately.
Notes
The chorizo breadcrumbs can prepared up to 3 days in advance.