Kyou no Ashura Meshi

One day, Omori Shizuka, a high school girl who loves to eat and is bullied, discovers the secret that Akira Kurose, aka "Ashura-kun," the only tough yankee at school, enjoys cooking.

Akira, a delinquent guy, likes a chubby girl for who she is, but he's worried about her health cause she's eating nothing but unhealthy food. The next day at lunchtime, Akira invites Shizuka to the rooftop and asks her to eat his homemade lunch box. He starts making lunches for her so her diet gets better and their romance begins.

(Source: MU, edited)