Adding sauces and flavorings are wonderful. Anything without calories or very low in calories would be great. Yes, you can use vegetable or other broth to cook veggies and add lots of seasoning, and even cook the starch along with the veggies and broth to make a stew, even adding 1/4 cup of red lentils to thicken, or you can just heat broth with seasoning and combine with the carb to make more of a soup and have veggies separate. For flavorings, you can pick something like:
- any fresh herb, chopped
- an herb blend with thyme, oregano, basil, etc.
- "Asian" with soy sauce, mirin, rice vinegar, seaweed, and even some powdered "peanut butter"
- spicy: use any hot sauce you like or you can use chilies, black pepper, etc.
- To get a curry flavor, use any combination of turmeric, cumin, coriander, cinnamon, ginger, etc.
- low fat salsa
- BBQ sauce (can be loaded with sugar and have oil so use sparingly)
- low fat cheeses like a sprinkle of parmesan or low fat feta cheese (use no more than one Tablespoon)
That should get you started - be creative and just make sure you're not adding too many extra calories which will slow your weight loss.