Okay, being curious about this, I went to their online nutritional site. Their stuff varies widely:
A plate of nachos is near the top of the range at 990 calories.
A burrito supreme waivers around 500 calories, depending upon whether you choose chicken or beef.
A grilled steak taco is only 160.
So you could have two tacos and a diet drink for lunch and only consume about 300 calories. IF you could keep that up, yes, you'd lose weight.