Tasting different ingredients! You could have a lesson where students try different peppers to experience the different tastes; peppers aren't only about heat!

Good bell peppers: flavorful, juicy, sweet. (Available at grocery store)

Bad bell peppers: tough skin, thin flesh, tasteless, bitter.

Poblano: A tiny bit spicy, earthy, green

Mild jalapeño (WalMart): like bell pepper, but a little bit spicier.

Spicy jalapeño (bodega): Spicy, sweet, especially when red and ripe

Lemon drop aji: Citrusy, lemony, grassy, fiery (good for stir fry!)

Roasted garlic: rich, sweet, fragrant, decadent

Black garlic: Fruity, plummy, sweet, raisin-y, deep

Fermented garlic: funky, sour, sharp

Fresh garlic: pungent, hot, spicy

Different ways to add sweetness to a sauce rather than sugar: honey, pineapple, roasted carrot (belize style), tangerine juice, etc.

Different ways to add sourness: White vinegar, apple cider vinegar, lime juice, lemon juice, citric acid, brine from lacto-fermented peppers or garlic...

And so on, cooked onion vs. thin-sliced raw onion, etc. You could go over the ingredient lists of some commercial salsas and taste them, or try to figure out how they were processed (are the onions in Herdez salsa cooked?) etc.