Cut cauliflower into florets and place in large bowl.
Slice grapes and place them in the bowl with the cauliflower.
Mince garlic and chop rosemary and add to bowl with the grapes and cauliflower.
Pour olive oil over cauliflower mixture.
Toss well. Spread cauliflower mixture onto a foil lined baking sheet, add a small pinch of salt and pepper, place in the oven at 425 degrees for 25 minutes. In the last 5 minutes of cooking, sprinkle chopped pecans across the sheet pan and continue to bake for remaining 5 minutes.