What could this cute girl promote? Of course: meat!
Meat is the best
いちばん written here in hiragana 一番 literally means number one or first in line. It is used to create superlative form of adjectives. Here the adjective is omitted leaving impression that meat is the best, meat is the most. Thus literal translation might be “meat is the …st”
肉 is a Chinese character for meat. It is meant to look like meat or muscles.
It is abbreviated to 月 in many characters related to body parts 腕 (an arm), 脚 (a leg), 腰 (a waist), and even 肝 (a liver) or 臓器 (internal organs) that rather do not have muscles.
What is confusing is that 月 as a part of a character comes from 3 different sources. It can mean 肉 meat, 月 the moon, or 舟 ship.