Asar vs. rostizar
The Spanish verbs asar and rostizar both refer to cooking food with dry heat, but they differ significantly in their regional usage and the specific cooking techniques they imply. While asar is a universal and broad term for various dry-heat methods, rostizar is a regional term that specifically highlights the use of a rotisserie or achieving a crispy oven-roasted exterior.
Asar
The word asar is the most universal and general Spanish verb used to describe roasting, grilling, or broiling. It is understood in all Spanish-speaking countries and applies broadly to cooking meats, vegetables, or fruits in an oven, over hot coals, or on an open grill.
Voy a asar la carne en la parrilla esta tarde.
(I am going to roast the meat on the grill this afternoon.)
Prefiero asar las verduras al horno con un poco de aceite de oliva.
(I prefer to roast the vegetables in the oven with a little olive oil.)
Mi abuela sabe cómo asar un cerdo entero para las fiestas.
(My grandmother knows how to roast a whole pig for the holidays.)
Podemos asar unas manzanas para el postre de esta noche.
(We can roast some apples for dessert tonight.)
Siempre es buena idea asar los chiles antes de pelarlos para hacer la salsa.
(It is always a good idea to roast the peppers before peeling them to make the salsa.)
Rostizar
The word rostizar is primarily used in Latin America, especially in Mexico, to describe roasting meat on a spit, rotisserie, or in a hot oven to achieve a brown, crispy skin. It is most famously associated with poultry, such as rotisserie chicken, though modern culinary trends also use it for oven-crisped vegetables.
Compramos un pollo entero para rostizar en la cena de hoy.
(We bought a whole chicken to roast for dinner today.)
El chef decidió rostizar el pavo lentamente para mantener la carne jugosa.
(The chef decided to slowly roast the turkey to keep the meat juicy.)
Me encanta rostizar la carne de cerdo hasta que quede crujiente por fuera.
(I love to roast the pork until it is crispy on the outside.)
Para esta receta debes rostizar los tomates y las cebollas durante media hora.
(For this recipe you must roast the tomatoes and onions for half an hour.)
Vamos a rostizar un pato con especias para celebrar nuestro aniversario.
(We are going to roast a duck with spices to celebrate our anniversary.)
Summary
In short, asar is your universal, go-to verb for grilling and oven-roasting any type of food anywhere in the Spanish-speaking world. Conversely, rostizar is predominantly a Latin American term that specifically evokes the image of rotisserie cooking or high-heat oven-roasting to get a crispy golden exterior, most notably applied to chicken.