In a food processor, pulse the spinach, cilantro, parsley, onion, garlic, cumin, salt, red pepper flakes, and paprika until finely diced. Do not form into a puree- the mixture should still have texture.
Add in the lemon juice, tahini, chickpeas, and flour. Pulse until the mixture reaches a consistency where it holds together when formed into a ball, but does not get too finely pureed.
Line a cookie sheet with wax or parchment paper. Roll falafels into 2 inch balls, then place on cookie sheet. Once finished, chill balls in freezer for 30 minutes to harden.
cook the falafel
Pour oil into a large caste iron pan until it reaches a depth of 1 inch. Heat to roughly 350°F.
Remove falafels from freezer and fry 5-6 falafels at one time. Cook for 30 seconds on one side, then continue to cook, turning occasionally, until the entire falafel is a deep golden brown. Repeat with remaining falafels.
make the sandwiches
Spread 2-3 tablespoons of beet hummus onto each pita. Top with a small handful of arugula, then 2-3 falafels, then yogurt.