There's a tilapia dish that is weight friendly. Also there are a variety of salads, not just the garden. There's fruit, watermelon, caprese, and maybe more. If your Sims eat healthy for a bit, they'll unlock the healthy living lifestyle which in turn unlocks more healthy recipes and quick meals. Sims can get super skinny if they eat this way all the time, so you may still want to have an occasional pasta dish. It helps to save the heavier meals for when Sims are in yellow or red for that need.
If you have the Cool Kitchen Stuff pack, there's ice cream that can cause either rapid weight loss or gain. This does tend to move to the extremes though.
Exercis, or lack of it, is another way to keep Sims in the shape you imagine them to be.
