Heat oven to 375°F (190°C). Halve pears lengthwise and remove cores with a small spoon, leaving enough flesh to hold their shape. Trim a very thin slice from the rounded underside if necessary to make each half sit flat.

Mix oats, walnuts, melted butter, maple syrup, cinnamon and salt until evenly damp. Brush cut pear surfaces with lemon juice.

Arrange pear halves cut side up in a snug baking dish. Divide crumble among the cavities, mounding lightly without covering every part of the fruit. Pour water into the dish around the pears.

Cover loosely with foil and bake 20 minutes. Uncover and bake 15–20 minutes more, until a small knife enters the thick flesh easily and topping is lightly golden. If the dish dries out, add a little hot water around the edges.

Rest 10 minutes so the fruit is warm rather than scorching hot. Serve one pear half per person with a little of the baking juices. Ice cream or yogurt is optional and not included in the nutrition estimate.