It is the first new project revealed by the London-based team since then, and will become Alsop's only built project on the African continent.
Proposed for central Nairobi, The Beacon is described by All Design as an open-air mall. It will contain 24,300 square metres of shops and restaurants, topped with a roof garden and bar.
According to the design team, the shopping centre is designed around the theme of a sweet factory to "fulfil Alsop's desire that architecture should always be fun".
The building's main facade will be typical of Alsop's bright and playful designs, with monochrome porcelain panels broken by a large red box.
Inside, the shopping centre will contain several fun flourishes. As well as the jellybean-inspired monorail and piano-key staircase, there will be fairground rides including a helter-skelter and a merry-go-round.
Walkways will be sheltered by colourful fabric canopies, while a rooftop canopies will boast a thatched roof.
"The Beacon is intended to bring delight to locals and tourists," said a statement from the practice. "The vivid colours and striking patterns of the facade will hint at the amusements and leisure facilities inside."
A seven-storey office tower will stand alongside the shopping centre. Both this and the shopping centre are backed by London- and Nairobi-based developer Kiloran, and are expected to complete in 2020.
"We were intrigued by Kiloran's ideas for this mall in Nairobi and were pleased to be able create an open-air mall with a focus on sustainability, fun and family which we believe to be key drivers on future international mall design," said Marcos Rosello, co-founder of All Design.
Will Alsop passed died on 12 May 2018, aged 70, following a short illness. Described as "one of architecture's biggest characters and talents", his legacy includes the turquoise Peckham Library in London and the stilted Sharp Centre in Ontario.
The Beacon marks the continuation of the work of All Design, which he founded in 2011. It joins a series of large-scale proposals for Nairobi, which has become a centre for Africa's tech innovations.
Other recent proposals in the city includes a 30-storey wedge-shaped tower by Richard Keep and Henry Goss. Meanwhile, Manhattan-based firm SHoP Architect is overseeing the masterplan for the under-construction Konza Techno City.
Architect: All Design
Design Team: Will Alsop, Marcos Rosello, Lucy Atlee, Amanda Callaghan, Kate Tseng, Ned Drury, Tom Bower, Helen Lee, Daniel Lee, Jacob Dix
Local architect: DMJ