。
My neighbor peeked just a little over the top of the fence.
Literal
Neighbor [subject-が] fence [possessive-の] top [from-から] a-little face [object-を] peeked.
ちょこっと is an informal diminutive of ちょっと — 'just a teensy bit.' 顔を覗かせた is a causative form meaning 'made (one's) face peek out' — the subject causes their own face to appear. 塀 (へい) is specifically a wall or fence around a property, not an interior wall. The scene is very Japanese — neighbors and property boundaries are a frequent setting in daily life.