Heat oven to 425 degrees F. Then, line a large baking sheet with aluminum foil or parchment paper. Add cauliflower florets to baking sheet and top with olive oil, thyme, salt and pepper. Using kitchen tongs or hands, toss until florets are well coated. Spread out into a single layer. Bake cauliflower about 20 minutes until tips and edges have turned golden brown, stirring and rotating halfway through baking. Scatter parmesan over cauliflower and place back into the oven for 5 minutes until cheese has melted and begins to brown. Remove from the oven and scatter with lemon zest and lemon juice on top.