Whisk the vinaigrette: In a small bowl, whisk olive oil, lemon juice, white wine vinegar, Dijon, honey, salt, and pepper until glossy and emulsified. Let it stand 10 minutes to mellow while you prep the rest.
Toast the nuts: Warm a dry skillet over medium heat. Add pecans and toast, stirring, until fragrant and slightly darkened, 3–4 minutes. Transfer to a plate to cool.
Cook the chicken: Heat a grill pan or skillet over medium-high heat. Add 1 teaspoon olive oil. Pat chicken dry and season both sides with a pinch of salt and pepper. Sear until golden and cooked through, 4–5 minutes per side (165°F internal). Rest on a board 5 minutes, then slice or chop bite-size.
Prep the produce: Slice strawberries, thinly slice cucumber, and dice avocado just before assembling to keep it fresh.
Dress the greens first: In a large bowl, toss the spring mix and cucumbers with 1–2 tablespoons of the vinaigrette and a tiny pinch of salt. Divide among plates or a large platter.
Finish and serve: Top dressed greens with warm chicken, strawberries, and avocado. Spoon over more vinaigrette to taste. Sprinkle with toasted pecans and goat cheese (if using). Crack a little black pepper on top and serve right away.