Preheat your BBQ (or indoor grill pan) over medium high heat.
Season the tri tip generously with kosher salt + pepper.
Grill the tri tip on the grill until it has an internal temperature of 125ºF for medium rare, about 8-10 minutes per side. Remove the tri tip from the heat and rest for 15 minutes.
While the tri tip is resting, make your salad dressing in the bottom of your salad bowl. Combine the olive oil, red wine vinegar, dijon mustard, and kosher salt + pepper to taste. Stir to combine. Add in the arugula, and toss.
After the tri tip has rested, slice against the grain. Add it on top of the arugula, and garnish with pickled onions.