Place the chopped cactus in a 2-quart (2lt) saucepan. Cover with water and bring to a boil over medium heat. Simmer for 5-10 minutes until the cactus turns from bright green to olive drab color. Remove the pan from the heat and pour through a colander to drain the water. Rinse the cactus under running water for 2-3 minutes until cool. 

Add the olive oil to a skillet and heat over medium heat. Add the tomatoes and lightly roast for 1 minute. Add the garlic and roast for 30 seconds. Remove the tomatoes and garlic and place in the container of a blender.

Fill a 1 qt. (1lt) saucepan with water and bring to a boil. Add the dried chile chipotle and simmer for 5 minutes until the chiles are soft. Add the chiles to the container of the blender. Puree until smooth.

Return the skillet to the heat. Add the chopped onion to the pan and sauté for 1-2 minutes until the onions become translucent. Add the cooked cactus and sauté for another minute. (Add 1-2 tbsp. (15-30ml) more olive oil if the vegetables seem dry.) Add the tomato chile puree and stir to combine well. Simmer for 2 minutes over medium heat until the sauce is reduced. Season with salt and pepper to taste.

Serve over roasted meats, vegetables, in quesadillas or over eggs.