Preheat grill burners over medium-high heat or to at least 450 degrees. Add the tomatoes to a cast iron skillet, drizzle with 1 tbsp. olive oil, and season with salt and pepper. Place cast iron in preheated grill. Cook tomatoes until blistered and they begin to pop, releasing their juices.

Add nuts to food processor and pulse until ground. Add basil, feta, minced garlic, lemon juice (if using) to food processor, and season with salt and pepper. Pulse until completely incorporated. Scrape down sides and drizzle in ⅓ cup of olive oil. Pulse until completely smooth.

Slice baguette and toast in toaster or on grill. Spread whipped feta pesto on bread, top with blistered tomatoes, and garnish with extra basil if using. Serve.