This salad feels like such a tribute to early summer that we wanted to bring it back in the same time of year as we did last in 2019. It's a combination that we turn to again and again as the weather warms up, particularly because all of the ingredients can be prepped ahead and served chilled.
Barley - (Skip if made ahead for Tuesday.) Bring a saucepan of water to boil. Salt water generously and add barley. Simmer for 45 to 55 minutes until tender but not soggy. (Can be done up to 5 days ahead)
Make vinaigrette - Whisk together mustard, honey, and vinegar. Add olive oil while whisking. (Can be done up to 5 days ahead)
Green beans - Chop green beans. (Can be done up to 5 days ahead)
Cook green beans - Place green beans in a microwave-safe bowl. Cover with a wet paper towel and microwave until tender, 3 to 5 minutes. (Can be done up to 5 days ahead)
Heat a skillet over medium heat. Add walnuts to dry skillet and saute until golden brown and fragrant, ~5 minutes. Set walnuts aside and return skillet to heat.
Increase heat to medium-high and add cooking oil. To heated oil, add chicken and saute until nearly cooked through, ~4 minutes. Add first part of vinaigrette and simmer until chicken is cooked through and vinaigrette cooks down, ~2 minutes more.
Assemble salads by creating a bed of lettuce in each serving bowl. Top with green beans, barley, plums, chicken, walnuts, and crumbled cheese. Finish with second part of vinaigrette. Enjoy!