Bring a large pot of water to a boil. Once boiling, season with 1 tsp kosher salt. Add the farro and boil 25-30 minutes, stirring occasionally to prevent sticking, until your desired al dente texture is reached. Drain & immediately rinse with cold water. Set aside to drain well or transfer to an airtight container & store in the refrigerator for up to 5 days.
Place the finely diced red onion in a small bowl & squeeze the lemon juice over top. Stir to combine & set aside to sit as you prepare the remaining ingredients. Slice the tomatoes, dice the cucumbers, & roasted red bell pepper, etc. Once all of your ingredients are prepped, drain the lemon juice from the onions & discard.
Combine all listed ingredients in a small bowl or jar. For a little kick of heat, sprinkle in a little crushed red pepper flake. Whisk or shake to combine. Taste and season with additional kosher salt or ground black pepper as desired. Set aside, or store in the refrigerator for up to 1 week.
To a large bowl, add the farro, red onion, tomatoes, cucumber, roasted red pepper, feta, chickpeas, & arugula. Pour the simple Greek vinaigrette over top. Toss to combine. Taste & adjust seasonings as desired. Enjoy!