- Preheat oven to 375°F.
- Sprinkle beef with 1/2 teaspoon salt and black pepper. Spray large ovenproof skillet with nonstick spray and set over medium-high heat until hot. Add beef and cook, turning occasionally, until well browned, about 10 minutes. Transfer skillet to oven and roast until instant-read thermometer inserted into center of beef registers 145°F, about 1 hour, adding tomatoes to skillet during last 10 minutes of cooking time. Transfer beef to cutting board and let stand 10 minutes. Transfer tomatoes to serving platter.
- Meanwhile, to make chimichurri, stir together cilantro, parsley, garlic, 2 tablespoons water, vinegar, red pepper flakes, lemon juice, and remaining 1/4 teaspoon salt in small bowl.
- To make pan sauce, place same skillet over medium-high heat. Add remaining 2 tablespoons water and cook, stirring to scrape up browned bits from bottom of pan, until mixture comes to simmer, about 2 minutes. Transfer to small bowl.
- Cut beef into thin slices and serve with tomatoes and chimichurri. Pass pan sauce at table.
- Per serving (about 3 ounces cooked beef, 1/3 cup tomatoes, 1 1/2 tablespoons chimichurri sauce, and 11/2 tablespoons pan sauce)
Tomatoes on the vine make a pretty presentation, but you can use 3 cups of regular cherry tomatoes or grape tomatoes if you wish.