This is now officially one of the best Vietnamese restaurants I've been to in Vegas. The inside is very clean and modern. There was about 3-4 other groups there during week day lunch hour. To start we all shared a hot tea ($1.50) which was good but had bits of tea...needles? in it that I had to keep spitting out. I had the Bun Bo Hue, a spicy noodle soup with beef and pork loaf. Pork loaf is.. interesting. It has the texture of fish cake and I assume the process to make it is similar. It didn't have a very strong taste and they give you a ton of slices but I couldn't manage to eat more than one or two. For this reason I wish they offered a vegetarian option but overall it was a good dish.
My coworkers had the Bun Xao and we all tried the BBQ pork banh mi. The Bun Xao looked and smelled delicious though I didn't get a taste. Definitely trying that next time. The BBQ pork looked a lot more appetizing than my pork loaf :( The banh mi was seriously awesome. It was stuffed with ingredients unlike other pho places in the area and they give you a big portion for the price. (I think it was $4.50 or something). I could easily grab one of these to go for a quick lunch.
Update: I've now found my favorite dish here and it's the tofu and vegetable pho. I get this pretty much everywhere but Sunflower has elevated my expectations. They don't just stick sliced tofu in the soup, they have what looks and tastes like marinated seitan, though I'm not positive it is. Either way it's so good. In addition they give you deep fried bean curd slices, shiitake mushrooms, carrot, zucchini, squash, and cabbage. It's like they actually care about the quality of vegetables they're serving you! The shiitake and bean curd add an umami that I've never had in pho and I'm in love. It's hearty and delicious and I can't recommend it enough.