For the Falafel: Drain the chickpeas through a colander then place on a baking sheet lined with paper towels to absorb any excess moisture. Chickpeas should be totally dry.
Heat 4-inches peanut or vegetable oil in a medium saucepan over medium heat until it reaches 330 degrees F on a deep-fry thermometer.
While the oil is heating, heat the olive oil in a small saute pan over medium heat. Add the garlic and serrano chiles and cook until soft, about 3 minutes.
Transfer the chickpeas to a food processor, add the garlic mixture, green onions, parsley, mint, cilantro, lemon juice, cumin, coriander, baking powder, salt and pepper and process until the mixture is finely ground, stopping to scrape the bowl every 30 seconds. Transfer the mixture to a bowl.
Line a baking sheet with paper towels. Form the mixture into balls the size of ping pong balls and place on a plate. Fry in batches at 330 degrees F until a pale blonde color, about 45 seconds, spooning oil over the falafel constantly. Remove with a slotted spoon to the baking sheet. Increase the heat of the oil to 350 degrees F. Return the falafel to the oil, in batches, cover the pan with a lid for 30 seconds and fry until a deep brown color, spooning the oil over the falafel constantly. Remove with a slotted spoon to baking sheet lined with paper towels, and immediately season with salt.
For the yogurt sauce: Place all ingredients in a blender and blend until smooth; season with salt and pepper to taste and transfer to a small bowl. Refrigerate for at least 30 minutes, covered, to allow the flavors to meld.
Variation: Substitute 2 cups feta cheese for the yogurt, and add 1/2 cup finely chopped parsley.
For the hummus: Place beans, garlic, harissa, lemon juice, and tahini in the bowl of a food processor and process until smooth. With the machine running, slowly add the olive oil until emulsified. Season with salt and pepper, to taste.
For the relish: Whisk the oil, vinegar, and smoked paprika in a small bowl. Add the remaining ingredients and toss. The tomatoes should be lightly dressed.
Serve falafel with yogurt sauce, hummus and relish on the side.