I used to make a lot of jam, one of the varieties was marrow and ginger, which I reckon you could adapt for cucumber. Recipe here:
Marrow, peeled de-seeded and chopped, half fine, half about 1/2" square - 1700g
Apple, (cooking apple type) peeled, de-cored, chopped - 850g
Crystallised ginger - I preferred chinese - chopped fine - 250g
Juice of 2-3 large lemons 150ml
White granulated sugar - I always used cheapest beet sugar -2000g
Allspice, powdered, 1/2 level teaspoonful.
You don't need water.
Put the chopped marrow in a bowl with half the sugar, stir and leave overnight in the fridge.
The following day, put the chopped apple in a bowl, loosely cover and microwave until it mashes into a soft pulp. Stir in the lemon juice and put to one side.
Put the marrow mixture (which by now will look very watery) in a thick bottomed pan with the chopped ginger and the rest of the sugar and heat gently, stirring until the sugar has completely dissolved. Cook further until the larger marrow pieces are transparent. Do not boil at this stage. Allow to cool slightly and then add the mashed apple and lemon juice mixture and the allspice. Stir in well.
Increase the heat very slowly, stirring all the time. Bring to a rolling boil until a temperature of 104-104.5 degrees C is reached and remove from heat stirring gently.
Jar and seal.
Makes about 7lb,
I guess the cucumber will have more water content than marrow, and be less dense, so I'd probably chop the cucumber a bit larger and increase the chopped apple to 1000g.