How to Make It
Combine onion, red wine vinegar, canola oil, and 1/4 teaspoon of the salt in a small bowl. Stir and let marinate 15 minutes at room temperature. Prepare farro according to package directions; set aside.
Heat a large nonstick skillet over medium-high. Add bacon; cook until crispy, 6 to 8 minutes. Transfer bacon to a plate lined with a paper towel, reserving 2 tablespoons of the bacon drippings in skillet. Return skillet to medium-high; add cherry tomatoes, squash, and 1/2 teaspoon of the salt. Cook, stirring occasionally, until tomatoes start to burst and squash is slightly tender and lightly golden on edges, 4 to 5 minutes. Add beans; stir to combine, and remove from heat.
Transfer onions from marinade to a plate, and reserve marinating liquid. Add 1 tablespoon of the olive oil to marinating liquid, and whisk until combined.
Assemble the salad: Toss together arugula, and remaining 2 tablespoons olive oil and 1/4 teaspoon salt; spread in an even layer on a large platter. Add cooked farro to skillet with vegetables and beans, and stir to combine; spoon farro mixture over arugula. Tear bacon into bite-size pieces. Scatter bacon, marinated onions, feta cheese, and pepper over salad; drizzle with dressing. Serve immediately.