What it means
Not spicy, please. Literally "don't want spicy."
When to use it
Spice levels vary wildly by region, so be specific: 微辣 (mild), 中辣 (medium), 特辣 (very spicy). 不要辣 usually means no chili at all.
Examples
zhè这dào道cài菜bú不yào要là辣。
Not spicy for this dish, please.
wǒ我bú不yào要là辣，xiè谢xie谢。
No spice for me, thanks.
yǒu有diǎn点là辣，qǐng请shǎo少fàng放là辣jiāo椒。
It's a bit spicy, please use less chili.
The full set of survival phrases for greetings, dining, shopping, and getting around, each with audio.