There's a reason why people in the hottest climates around the world--particularly those in India & Africa--wear tunics: they're easy & cool.
Here in the States, tunics have come in & out of favor. A sweeping craze for them about eight summers ago faded; they're just beginning to come back, & I've pulled out all my old ones. You'll find new ones now sometimes listed as "swim cover-ups," & they're often surprisingly affordable.
You might also try visiting an Indian store to find one; many tunics are made in India anyway. A tunic may also be called a kurta or kaftan. Most traditional Indian tunics are longer, more colorful, & more intricately embroidered than the American styles.
Tunics can have a boho feel to them or look more conservative--I like both styles. Wear them fitted, not tent-like :-). I think they're cutest with mid-thigh shorts. I believe tunics are perfectly work-appropriate with white pants or crops. I'm partial to tunics made of cotton with long or 3/4-length sleeves.
From Calypso St. Barth
Many more tunics from Calypso St. Barth at all prices & styled with white skinnies & shorts here.
From J. Crew Factory
From Piperlime. Many more Piperlime kurtas here.
From Old Navy
From Tea Collection
If you want to look put together when you're melting down, a tunic might be the answer. Do you agree?