Slice the pineapple into 1-inch chunks. Set some aside for garnishing. Add pineapple, ice, tequila, triple sec, lime juice, and agave to a blender and blend until smooth.
In a shallow dish, mix together the cinnamon and sugar.
Run a small amount of agave around the rim of each glass and dip it into the cinnamon sugar mixture.
Pour the blended mixture into two glasses and garnish each with a chunk of pineapple and a slice of lime.
Optional: Sprinkle some cinnamon sugar over the top of the margarita for an extra dose of sweetness.