Place tarragon sprigs, halved shallot, smashed garlic, and chicken in a medium saucepan. Add water to cover by 1 inch and season with salt and pepper. Bring water to a boil; remove pan from heat, cover, and let stand until chicken is just cooked through, 15–25 minutes, depending on size of chicken breasts. Transfer chicken to a plate and let cool. Shred or dice chicken.
Meanwhile, whisk yogurt, oil, minced shallot, and minced garlic in a small bowl. Season dressing with salt and pepper.
Combine all peas in a medium bowl. Add chicken, dressing, minced tarragon, parsley, chives, lemon zest, and 1 Tbsp. lemon juice; toss to coat. Season to taste with salt, pepper, and additional lemon juice, if desired. Serve spooned over toasted bread and/or lettuce leaves.
Place tarragon sprigs, halved shallot, smashed garlic, and chicken in a medium saucepan. Add water to cover by 1 inch and season with salt and pepper. Bring water to a boil; remove pan from heat, cover, and let stand until chicken is just cooked through, 15–25 minutes, depending on size of chicken breasts. Transfer chicken to a plate and let cool. Shred or dice chicken.
Meanwhile, whisk yogurt, oil, minced shallot, and minced garlic in a small bowl. Season dressing with salt and pepper.
Combine all peas in a medium bowl. Add chicken, dressing, minced tarragon, parsley, chives, lemon zest, and 1 Tbsp. lemon juice; toss to coat. Season to taste with salt, pepper, and additional lemon juice, if desired. Serve spooned over toasted bread and/or lettuce leaves.