In a medium bowl, combine the coarsely chopped tomatoes, shredded coconut, minced green chilis, salt, and yogurt.
Stir well until everything is evenly mixed.
Prepare the tadka (tempering).
Heat the vegetable oil in a small skillet over medium-high heat.
Add the whole mustard seeds and crushed red pepper and fry until the seeds begin to pop and sputter, about 30-60 seconds. Immediately pour the hot oil and spices into the yogurt mixture and stir quickly to combine.
Cover and chill the raita in the refrigerator for at least two hours before serving to allow the flavors to fully develop and meld together.
Don't skip the chilling step! Allowing the raita to rest for a few hours is crucial for the flavors to meld together beautifully.