Put Romanesco florets in a steamer basket and set in a large pot filled with 1/2 in. water. Steam over medium-high heat until tender-crisp, 8 to 10 minutes. Transfer to a colander and rinse with cold water.
Whisk vinegar, oil, orange zest and juice, capers, salt, and pepper in a large bowl. Add remaining ingredients and stir to coat.
Note: Nutritional analysis is per serving.