Lechon asado con plátanos--cuban pork roast with plantains

Ingredients

• 1 4 pound pork shoulder
• 3 teaspoons jarred garlic
• 1/2 tablespoon salt
• 3/4 teaspoon oregano
• 3/4 teaspoon ground cumin
• 1/4 teaspoon ground black pepper
• 1/2 tablespoon olive oil
• 1 large onion, sliced
• 1/4 cup lime juice
• 1/4 cup orange juice