Add cauliflower and chopped onion to skillet; cook about 2 minutes or until lightly browned, stirring frequently. Add garlic, thyme, salt, and pepper; cook and stir 30 seconds more. Add lemon juice, stirring to scrape up any browned bits in pan. Add the 1 teaspoon lemon zest and the broth. Bring to boiling; reduce heat. Simmer, covered, 6 to 8 minutes or until cauliflower is tender. Remove from heat.